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Originally published in Science Express on 3 April 2003
Science 2 May 2003:
Vol. 300. no. 5620, pp. 789 - 791
DOI: 10.1126/science.1081311
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Reports

Iron Partitioning in Earth's Mantle: Toward a Deep Lower Mantle Discontinuity

James Badro,1 Guillaume Fiquet,1 François Guyot,1 Jean-Pascal Rueff,2 Viktor V. Struzhkin,3 György Vankó,4 Giulio Monaco4

We measured the spin state of iron in ferropericlase (Mg0.83Fe0.17)O at high pressure and found a high-spin to low-spin transition occurring in the 60- to 70-gigapascal pressure range, corresponding to depths of 2000 kilometers in Earth's lower mantle. This transition implies that the partition coefficient of iron between ferropericlase and magnesium silicate perovskite, the two main constituents of the lower mantle, may increase by several orders of magnitude, depleting the perovskite phase of its iron. The lower mantle may then be composed of two different layers. The upper layer would consist of a phase mixture with about equal partitioning of iron between magnesium silicate perovskite and ferropericlase, whereas the lower layer would consist of almost iron-free perovskite and iron-rich ferropericlase. This stratification is likely to have profound implications for the transport properties of Earth's lowermost mantle.

1 Laboratoire de Mine Université ralogie–Cristallographie de Paris, Université Paris VI, Université Paris 7, CNRS, IPGP, 4 place Jussieu, F-75252 Paris Cedex 05, France.
2 Laboratoire de Chimie Physique–Matière et Rayonnement (UMR 7614), Université Paris VI, 11 rue Pierre et Marie Curie, F-75231 Paris Cedex 05, France.
3 Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Road, N.W., Washington, DC 20015, USA.
4 European Synchrotron Radiation Facility (ESRF), B.P. 220, F-38043 Grenoble Cedex, France.

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Science. ISSN 0036-8075 (print), 1095-9203 (online)